1. Field of the Invention
This invention relates to a simplified measuring device that provides a continuous visual indication of the current pressure range of a pneumatic tire or other pressurized device, container or vessel.
More particularly, the present invention relates to a pressure measuring assembly that is brought into fluid (air) communication with the interior pressure in a pressurized or pneumatic device and indicates pressure changes in the pressurized or pneumatic device by inducing a change from a first indicator state to a different indicator state evidenced by a change in pattern and/or color of the measuring assembly.
2. Description of Related Art
Maintaining the proper air pressure in pneumatic vehicle tires is critical for the safe and efficient operation of the tire as well as the vehicle as a whole. If such a tire is operated at air pressures above or below its recommended design pressure, the likely effects include; (1) substantially shortened life expectancy of the tires; (2) dangerous impairment to road traction and steering control required for safe vehicle operation; and (3) reduced overall vehicle fuel and mechanical efficiency.
It is clear that the effects of improperly maintained tire pressure can lead to loss of vehicle control (potential fatalities, injuries and property loss) and a significant increase in on-going vehicle operating expense (tires, fuel, etc.).
The proper maintenance of tire pressure has and continues to be an unsolved problem for the vast majority of vehicle owners and operators. Manually checking the pressure of each tire on a regular basis is both a nuisance and inconvenience to the average vehicle operator. The increase in popularity of "self-service" gas stations and the reluctance of service station attendants to "check the tires" only exacerbate this problem. This results in the majority of vehicle tires going unchecked, typically until abnormal tire wear is observed or vehicle handling becomes noticeably impaired.
As evidence of the long-felt need of the motoring public for a solution to this problem, one need only review the number of patents claiming to address this expensive and potentially dangerous situation. Numerous devices have been proposed and patented for providing a continuous and visible indication of tire operating pressure. Most of the prior art designs either replace the standard tire valve stem or are a replacement for the original valve cap (utilizing the existing standard valve stem). Given that the vast majority of car or truck owners would more readily replace a tire valve cap than a tire valve stem, attention will be directed towards the former. A partial list of United States Patents for devices for monitoring tire pressure are: U.S. Pat. Nos. 5,641,902; 5,569,849; 5,557,256; 5,115,832; 5,007,365; 4,819,686; 4,606,391; 4,464,929; 4,174,673, 4,116,157, 4,103,549, and U.S. Pat. No. 3,889,530.
Certain features appear to be critical for a commercially viable design: (1) minimize material fatigue and subsequent component failure; (2) minimize the effect or consequences of seal leakage or blow-by; (3) minimize the number of components, their costs and manufacturing complexity; (4) maximize the visual indication of the current operating conditions and the sensitivity to pressure changes; and (5) minimize the size and weight to be aesthetically pleasing and to not adversely affect the wheel's balance.
All prior art can be graded and ranked on their attempts to satisfy these fundamental design criteria. A careful review of the prior art, documents various techniques implemented to attain low complexity and high reliability. However when judged on the basis of balancing the delivery of high functionality (usability) within the constraints of a very small form factor, all the prior art falls significantly short of the goal. The following examples and discussion will highlight the difficulties of achieving an appropriate balance between functionality, reliability and aesthetically pleasing packaging.
Numerous references of prior art, (U.S. Pat. No. 5,007,365 for example) describe a pressurized chamber and piston which has been biased with a spring to movably respond to changes in operating pressure. This design when utilized in a continuously indicating device, subjects the piston seals to a constant pressure gradient under harsh environmental conditions. These environmental conditions include temperature extremes, moisture and other contaminates introduced by compressed air sources, and extreme pressure excursions as when the tire strikes a curb or other tire deforming obstruction. These environmental factors are particularly hazardous to seals and their ability to prevent leakage or blow-by, and thus compromise the integrity of the pressure measurement.
Alternatively to pistons and seals, U.S. Pat. No. 4,606,391 discloses a design incorporating the use of a flexible diaphragm to transmit pressure conditions between the tire and tire cap gauge. Two different configurations of diaphragms are noted in the prior art. One configuration allows for air pressure on the tire side of the diaphragm to stretch and elastically deform the diaphragm relative to the ambient pressure on the cap side of the diaphragm. The tire pressure acting on the diaphragm causes a displacement in the axial direction that is proportional to the pressure differential and this displacement is converted into a visual indication. While the inherent piston and seal disadvantages described previously are mostly overcome, this technique continually loads the diaphragm elastically, and given the likelihood of pressure spikes as noted previously, it significantly increases the probability of material fatigue or failure. The second method of incorporating flexible diaphragms while similar in configuration to the first, does not load the diaphragm elastically (in fact the diaphragm may be totally inelastic). Although the loosely fitting flexible diaphragm does hermetically divide the pressure chamber and allows for the transmission of pressure differential forces, it does so without putting a continuous elastic load on the diaphragm material. This technique overcomes many of the previously noted disadvantages of the elastically loaded diaphragm and requires much less precision construction and expense to produce than the sealed piston described earlier.
The ability of a device to deliver a continuous and highly visible indication of pressure change is critical to meeting consumer expectations. Designs that only marginally support this requirement will not be perceived as useful or convenient by the public regardless of the device's other technical merits. U.S. Pat. No. 4,819,686 discloses a tire cap design that while technically sound (its diaphragm is subjected to only the pressure differential between actual tire pressure and an initially set reference pressure) it only marginally meets the visual notification requirement. This and other prior art disclosures have positioned the visual indication to be most readily viewed from the end of the cap (apex or top). These designs neglect the fact that on most tires it is the sides of the cap that represent the predominant viewable surface.
U.S. Pat. No. 5,007,365 is a good example of the tradeoff inherent between visual sensitivity and device size or complexity. In this design, the tube body and spring constant must be sized to allow a sufficient displacement of the piston to provide a discernable visual pressure indication. For linear springs, this generally results in longer spring lengths to achieve the pressure change sensitivity capable of being visually detected. These spring lengths require longer tube bodies that critically lack esthetical appeal. Other designs require the vehicle operator to be positioned in very close proximity to the tire gauge (i.e., squat down or bent over) in order to discern the current pressure condition. These designs will simply not meet the ease of use and convenience requirement that the public expects.
It is evident that the prior art has failed to disclose a successful design for a purely mechanical device that is capable of displaying a highly visual indication of tire pressure in a very small form factor. While all prior art claim to satisfy one or more of the aforementioned design criteria, no prior art has been able to broadly satisfy all of them to the reasonable satisfaction of a manufacturer or the consumer. Thus, due to the lack of any significant commercial success of any previously patented design, it is clear that a highly functional, cost effective and easy to use device has yet to be disclosed.
In response to the numerous disadvantages of the prior art, the present invention is disclosed incorporating a new and novel visual indication feature without sacrificing any of the aforementioned design criteria.